Error in inserting a record in to table

Question

hi..
i created a trigger....when i am trying to insert new record in to table i am getting the fallowing error...plz kindly help me out from this...
SQL> create or replace trigger secure_emp
2 before insert on employees begin
3 if(to_char('sysdate','DY') in ('SAT','SUN')) or
4 (to_char('sysdate','HH24:MI') not between '8:00' and '18:00') then
5 raise_application_error(-20500,'error');
6 end if;
7 end;
8 /
Trigger created.
SQL> insert into employees(employee_id,last_name,first_name,email,hire_date,job_id,salary,department
_id)
2 values (300,'smith','jack','SJACK',sysdate,'IT_PROG',4500,60);
insert into employees(employee_id,last_name,first_name,email,hire_date,job_id,salary,department_id)
ERROR at line 1:
ORA-06502: PL/SQL: numeric or value error: character to number conversion error
ORA-06512: at "SCOTT.SECURE_EMP", line 2
ORA-04088: error during execution of trigger 'SCOTT.SECURE_EMP'

Answer 1

Yeah. Whenever Oracle sees TO_CHAR('string_literal1', 'string_literal2), it implicitly converts it to TO_CHAR(TO_NUMBER('string_literal1'), 'string_literal2). That's why an error in trigger occurs.
SQL> explain plan for
  2  select null
  3    from dual
  4   where dummy = to_char('A', 'DY');
Explained
SQL> @utlxpls
Cannot SET MARKUP
PLAN_TABLE_OUTPUT
Plan hash value: 397561404
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT  |      |     1 |     2 |     2   (0)| 00:00:01 |
|*  1 |  TABLE ACCESS FULL| DUAL |     1 |     2 |     2   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   1 - filter("DUMMY"=TO_CHAR(TO_NUMBER('A'),'DY'))
13 rows selected